Refrigeration control system



April 1, 194? G. H. FISHER REFRIGERATION CONTROL SYSTEM Filed Sept. 30,1938 ihwmtov Patented Apra Tl,

PATEN T REFRKGERATKON CCQNTRQIL SYSTEM George H. Fisher, ltiinneapolis,Minn, assignor to Minneapolis-Honeywell Regulator (Company,

Minneapolis, Minn, a corporation of Delaware Application September 80,1938, Serial No. 232,606

Claims.

This invention relates to refrigeration control systems and toimprovements in the component parts thereof.

The primary object of this invention is to provide an improved controlarrangement for a refrigerating apparatus which cools a plurality offixtures or zones wherein desired temperature conditions are at alltimes maintained in each fixture or zone, wherein the cooling coils ofall of the fixtures or zones are defrosted at each cycle of operation ofthe refrigerating apparatus, wherein too great a reduction of pressureon the low pressure side of the refrigerating apparatus is prevented,wherein the building up of extremely high head pressures is prevented,wherein starting of the compressor against relatively high headpressures is prevented, wherein defrosting of the coils of all of thefixtures or zones is assured at least at predetermined intervals in casethe cooling load in the various fixtures or zones tends to maintain therefrigerating apparatus in continuous operation, and wherein overheatingof the compressor motor is prevented by opening the energizing circuitof the compressor motor regardless of whether the overheating isoccasioned by overloading of the compressor motor or by the occurrenceof a decrease in potential difference across the energizing circuit ofthe compressor motor, the arrangement being such that if the energizingcircuit is opened by an overload condition manual reclosing is requiredbut if it is opened by a decrease in potential difference it is reclosedautomatically.

Further objects of the invention are to provide novel controlarrangements forming parts of the improved complete control arrangementoutlined above.

For a more thorough understanding of this invention reference is made tothe accompanying drawing in which:

Figure l is a diagrammatic illustration of the complete control systemof this invention as applied to a multiple fixture or zone refrigeratingapparatus,

Figures 2 and 3 are partial views showing the overload cut-out mechanismof Figure 1 in various operative positions.

Referring now to Figure 1 a plurality of fixtures or zones to be cooledare illustrated at H], H, and I2. rooms, walk-in boxes, show counters,or any other type of device which it be desired to cool. The fixtures orzones 10, II, and [2 are provided with cooling coils 13, It, and 15preferably in the form of evaporators for cooling the same. RefrigerantThese fixtures or zones may be is supplied to and withdrawn from theevaporators 53, i i, and i5 by means of a refrigerating apparatusgenerally designated at l E. The refrigerating apparatus may comprise acompressor ll operated by an electric motor 8 8. Compressed refrigerantleaves the compressor ll through a high pressure line 119 and flows intoa condenser 26 wherein it is condensed. Condensed refrigerant iscollected in a receiver 2i and then flows through a liquid line 22 andbranch liquid lines 23, 2 5, and 25 into the evaporators i3, M, and i5,respectively. Expanded refrigerant is Withdrawn from the evaporators i3,i l, and 55 through a low pressure or suction line 26 by the compressorEl. It is here noted that the evaporators it, i l, and 95 are arrangedin parallel relationship. Expansion valves 27, 28, and 29 control thesupply of refrigerant flowing to the evaporators it, Hi, and 15,respectively, and these expansion valves may be of the thermostatic typeprovided with a bulb located at the discharge of the evaporators andconnected by a capillary tube 38 to the expansion valves. Since theconstruction outlined above is generally old in the art a furtherdescription of the above is not considered necessary.

Located in the branch liquid lines 23, 26, and 25 are solenoid valves35, 36, and 37 for turning on or turning oil the supply of refrigerantto the evaporators l3, M, and 95, respectively. When the solenoid valves35, 36, and 31 are energized, refrigerant is supplied to theirassociated evaporators and when the solenoid valves are deenergizedfthesupply of refrigerant to their associated evaporators is shut off. Thezones or fixtures If], H, and 12 are provided with temperatureresponsive control means in the form of thermostats 38, 39, and it,respectively. The thermostat 38 may comprise a bellows 52 charged with avolatile fluid for operating a lever 43 against the action of anadjustable tension spring 44. The lever 43 operates a mercury switch 45provided with electrodes 46, M, and 48. For purposes of illustration itis assumed that when the temperature within the fixture ll] rises to 42,the switch 45 is tilted to a position to bridge the electrodes as, M,and [i8 and when the temperature decreases to the switch is tilted tothe position shown to unbridge the electrodes. The construction andoperation of the thermostats 39 and 40 are exactly the same as that ofthermostat 38 and consequently like reference characters for like partshave been utilized.-

A relay or starter for the compressor motor [8 is generally designatedat and may comprise an operating coil 5! for operating switch arms 52and 53 with respect to stationary contacts 56 and 55. The arrangement issuch that when the operating coil 5i is energized the switch arms 52 and53 move into engagement with their respective contacts 55 and 55 andwhen the operating coil 5| is deenergized the switch arms 52 and 53 aremoved out of engagement with their respective contacts by means ofsprings, gravity or other means (not shown).

The thermostats 38, 39, and 60 in addition to controlling theenergization of their associated solenoid valves 35, 36, and 31 alsocontrol the operation of the relay 0r starter 50 and hence the operationof the compressor ll. The relay or starter 50 is also controlled bycontrol means 51 and 58 responsive to the pressure on the high pressureside of the refrigerating apparatus, by control means 59 and 60responsive to the pressure on the low pressure side of the refrigeratingapparatus, by an overload cut-out mechanism 6| responsive to the currentflow in the energizing circuit of the compressor motor I8 and by a timergenerally designated at 62.

The control means 51 responsive to pressure on the high pressure side ofthe refrigerating apparatus may comprise a bellows 65 connected by apipe 66 to the high pressure line IQ for operating a lever 61 againstthe action of an adjustable tension spring 68. The lever 51 operates amercury switch 89 the parts being so arranged that the switch 69 ismoved to closed position when the pressure on the high pressure side ofthe refrigerating apparatus decreases to 140 pounds and moves to openposition when the pressure increases to 145 pounds. The control means 51operates to determine at what pressure on the high pressure side of therefrigerating apparatus the compressor motor l8 may be placed inoperation.

The control means 58 may comprise a bellows 10 connected by the pipe 66to the high pressure line IQ for operating a lever ll against the actionof an adjustable tension spring I2. The lever 1| operates a mercuryswitch 13, the parts being so arranged that the switch I3 is moved toopen position when the pressure on the high pressure side of therefrigeratin apparatus rises to 200 pounds and to closed position whenthe pressure decreases to 195 pounds. The control means 58 determines atwhat pressure on the high pressure side of the refrigerating apparatusthat the compressor motor !8 is stopped.

The control means 59 may comprise a bellows U3 connected by a pipe tothe low pressure or suction line 26 for operating a lever 16 against theaction of an adjustable tension spring 11. The lever 16 operates amercury switch 18 to close the switch when the pressure on the lowpressure side of the refrigerating apparatus rises to 38 lbs. and toopen the switch when the pressure decreases to 33 lbs, For purposes ofillustration it is assumed that the pressure on the low pressure side ofthe refrigerating apparatus rises to 38 pounds only after defrosting ofall of the evaporators I3, l6, and I5 has occurred. The control means 59operates to prevent operation of the compressor motor 3 until thepressure on the low pressure side of the 'refrigerating apparatus hasrisen to a value indicating that defrosting of all of the evaporatorshas occurred.

The control means 60 may comprise a bellows 19 connected by the pipe 15to the low pressure or suction line for operating a lever 80 against theaction of an adjustable tension sprin The lever operates a mercuryswitch82, the parts being so arranged that the switch 82 is moved to openposition when the pressure on the low pressure side of the refrigeratingapparatus decreases to 10 lbs, and is moved to closed position when thepressure increases to 15 lbs. The control means 80 determines thepressure on the low pressure side of the refrigerating apparatus atwhich the compressor motor I8 is stopped.

The overload cut-out mechanism 8i comprises a movable contact 85 and astationary contact 88 which are in engagement during normal operation ofthe refrigerating apparatus. occurrence of an overload condition thecontacts 85 and 86 are separated in a mannerto be pointed out more fullyhereafter.

The timer generally designated at 62 may comprise a rotor 88 operated bya field winding 89 connected across line wires I00 and I0! leading fromsome source of power (not shown). The

rotor 88 operates a cam 9| through a reduction" gear train 90, the cam9! being provided with a high dwell for operating a lever 92 which inturn operates a mercury switch 93. For purposes of illustration it isassumed that the parts are so arranged that the mercury switch 93 ismoved to open position for a short interval of time every six hours.

Assume now that the temperature within the fixture or zone I0 rises to42 whereupon the switch as is tilted to a position to bridge theelectrodes 66, ll, and 68; a circuit is thereupon completed from theline wire I00 through wire I02, electrodes 46 and 48, wire I03, solenoidvalve 35 and wire I08 back to the other line wire I01. Completion ofthis circuit energizes the solenoid valve 35 to supply refrigerant tothe evaporator l3 within the fixture or zone Hi. When the temperaturewithin the fixture or zone It decreases to 40 to open the switch t5 thesolenoid valve 35 is deenergized to shut off the supply of refrigerantto the evaporator l3. In this manner the solenoid valve 35 is operatedto maintain desired temperatures within the fixture or zone ill. Thethermostat 39 and solenoid valve 36 are connected together and to theline wires I00 and lill in exactly the same manner as the thermostat 38and solenoid valve'35 and accordingly like reference characters primedhave been utilized for like connections. Also the thermostat 38 and thesolenoid valve 3'? operate in the same manner and accordingly the wiringconnections have been designated by like reference characters doubleprimed. Summing up, when any thermostat in any of the fixtures or zonescalls for cooling, its associated solenoid valve is opened to supplyrefrigerant to its associated evaporator to maintain desiredtemperatures in all of the fixtures or zones,

Assume now that the high pressure decreases to lbs. whereupon theswitches 59 and 13 of the control means.51 and 58 are closed, that thepressure on the low pressure side of the refrigerating apparatus risesto a defrosting value of 38 lbs. whereupon the switches 18 and 82 of thecontrol means 59 and 60 are closed, and that the temperature within thefixture or zone In rises to 42 to close the switch 45. A circuit isthereupon completed from the line wire I00 through wire I02, electrodes46 and 41, wires I06, I07, and I08, mercury switch 93, wires I09 and H0,mercury switch 69, wire Ill, mercury switch 78, wires H2 and H3,contacts 86 and 85 of the overload cut-out mechanism 8|, wire H4,operating coil 5|, and wire H5 back to the other line Upon the wire ll.Completion of this starting circuit energizes the operating coil 5i tomove the switch arms 52 and 53 into engagement with their respectivecontacts 54 and 55.

Movement of the switch arm 53 into engagement with the contact 55completes an energizing circuit for the compressor motor i8 which may betraced from the line wire I08 through wires H8, H9, and I20, heater l2I,wire I22, switch arm 53, contact 55, wire I23, compressor motor I 8, andwires I24 and I25 back to the other line wire IOI. Accordingly when theoperating coil M is energized the compressor motor I8 and hence therefrigerating apparatus is in operation.

Movement of the switch arm 52 into engagement with the contact 54completes a maintaining circuit for the operating coil 5| of the relayor starter 50 which is independent of the switches 89 and I8 of thecontrol means 5! and 59,, respectively. This maintaining circuit may betraced from the line wire I through wire I02, electrodes 46 and 41 ofthe thermostat 38, wires I 08, I01, and I08, mercury switch 93, wiresI09 and I28, mercury switch I3, wire I29, mercury switch 82, wire I30,contact 54, switch arm 52, wire H3, contacts 86 and 85, wire I I4,operating coil i, and wire I I5 back to the other line wire I0l.Completion of this-circuit maintains the operating coil 5I energizeduntil any of the switches 45, I3, 82, or 93-are opened, or until thecontacts 85 and 88 of the overload cut-out mechanism 6I.are separated.The electrodes 46 and 47 of the switches 45 of the thermostats 39 and 40are connected in parallel with the electrodes 46 and 4! 'of thethermostat 38, these parallel connections being shown by I02 and I06 forthe thermostat 39 andl02" and I06 for the thermostat 40.

, Summing up two circuits are provided for controlling the energizationof the operating coil 5|, a starting circuit including the switches 45of the thermostats 38, 39, and 40 connected in parallel, the switch 93of the timer 62, the switches 69 and I8 of the control means 51 and 59and the contacts 85 and 86 of the overload cut-out 6|. The other circuitis a maintaining circuit which includes the switches '45 'of thethermostats 38, 39, and 40 connected in parallel, switch 93 of the timer62, the switches 13 and 82 of the controLmeans 58 and 60, themaintaining switch formed by the switch arm 52 and contact 54 of therelay or starter 50, and the contacts 85 and 85 of the overload cut-outmechanism 6|. The operating coil 5| of the relay maybe energized andhence the relay pulled inonly when the starting circuit is completed andit is maintained energized, after it has once been energized by thestarting kcircuit, so long as the maintaining circuit is completed.Accordingly, the operating coil 5| .of the relay or starter may beenergized to operate the compressor I! only when any of the thermostats38, 39, and 40 are calling for cooling, the timer switch 93 is closed,the pressure on the high pressure side of the refrigerating apparatushas decreased to 140 pounds to close the switch 68, the pressure on thelow pressure side of the refrigerating apparatus has risen to adefrosting value of 38 lbs. to close the switch I8,and the contacts 85and 86 of the overload cut-out BI are closed. Hence the refrigeratingapparatus can only be started after defrosting of all of the evaporatorshas taken place and when the pressure on the high pressure side of therefrigerating apparatus has reduced to a predetermined low value whichgreatly reduces the starting load on the compressor motor I8 and henceeliminates the majority of the starting overload conditions.

After the compressor I? has been placed in operation in the mannerpointed out above, it will remain in operation until either all of thethermostats 33, 39, and 00 are satisfied, or the switch 93 of the timer62 is opened, or the pressure on the high pressure side of therefrigerating apparatus rises to 200 lbs. to open the switch I3, or thepressure on the low pressure side of the refrigerating apparatusdecreases to 10 lbs. to open", the switch 82, or the contacts and 88separate upon the occurrence of an excess current fiow in the energizingcircuit of the compressor motor.

The system thus far described controls the operation of therefrigerating apparatus to maintain at all times desired temperatureconditions in the various fixtures or zones I0, II, and I2, to providedefrosting of all of the evaporators 53, I4, and I5 at each cycle ofoperation of the compressor IT, to prevent too great a reduction ofpressure on the low pressure side of the refrigerating apparatus, toprevent thebuilding up of extremely high pressures on the high pressureside of the refrigerating apparatus and to prevent starting of thecompressor against relatively high head pressures. Ordinarilythermostats 38, 38, and 48 will tend to call for cooling atsubstantially the same times and will tend to be satisfied atsubstantially the same times so that intermittent defrosting of theevaporators I 3, I4, and I5 will occur. However, it is quite possibleunder certain operating conditions that at least one of the thermostats38, 39, and 40 will be calling for cooling at the same time and afterthe compressor is placed in operation it will remain in operation for along period of time tending to build up frost on the evaporators I3, I4,and I5. The timer operating the switch 93 is utilized for shutting downthe refrigerating apparatus at predetermined times, say every six hours,and after the refrigerating apparatus has been shut down in this mannerit is impossible to restart the same until the suction pressure hasrisen to the defrosting value of 38 lbs. Accordingly defrosting of theevaporators -I3, I4, and I5 at least every six hours is provided. Inother words, the timer 62 operates to insure that the evaporators I3, I4and I5 will be defrosted at least at predetermined times although theevaporators are usually defrosted more often than this.

The overload cut-out mechanism BI may comprise a support I32 carrying apivot I33. A lever I34 is carried by the pivot I33 and is urgeddownwardly by a spring I35 into engagement with the end of a bimetallicelement I36 also secured to the support I 32. Levers I31 and I38 arefulcrumed on the support I32 and are connected together by an overcenterspring I39. The lever I31 carries an insulating pad I40 upon which aremounted the movable contact 85 and a movable contact I4I which isadapted to engage a stationary contact I42. The lever I34 is providedwith a slot I43 for receiving the end of the lever I38. With the partsin the position shown in Figure l, the lever I34 is engaging thebimetallic element I36 and the overcenter spring I 39 holds the movablecontact 85 in engagement with the stationary contact 86. If now thecurrent flow in the energizing circuit for the compressor motor I8should become excessive, the heater element I2I will heat the bimetallicelement I35 and warp the same outwardly to the position shown in Figure2. Outward movement of the bimetallic element I36 releases the lever I34and the spring I35 moves the same downwardly. Downward movement of thelever 1313 causes the lever I38 to move downwardly to move the springI39 overcenter, which in turn causes the contacts 85 and 85 to separatewith a snap action and causes contacts IQI and I 32 to make with a snapaction. Separation of the contacts 85 and 86 in this manner interruptsthe above outlined starting and maintaining circuits for the operatingcoil I to drop out the relay or starter 5'0 and stop operation of thecompressor motor I8.

An auxiliary lever MB is secured to the main lever I31 by a pivot M1,the auxiliary lever being maintained normally in the position shown inFigures 1 and 2 by a compression spring M8. The lever I M5 is providedwith an extension I419 which is adapted to be engaged by an abutment I56which is secured to a button I5I. A compression spring I52 locatedbetween the button I5I and a stationary support I53 maintains theabutment I50 in the position shown in Figures 1, 2, and 3. After theoverload cut-out mechanism 61 separates the contacts 85 and 85 in themanner outlined above, the overload cut-out mechanism may be restored tothe position shown in Figure 1 by pressing inwardly on the button I5I.This raises the lever I34 about its pivot I33 and allows the bimetallicelement I36 to again move under the lever I3 1 to hold the parts in theposition shown in Figure l.

A stationary contact I55 is secured to a suitable support I58 and amovable contact I51 is secured to a support I58. An armature I59 issecured to the movable contact I51 and is influenced by a winding I60,connected by wires ISI and I52 across line wires I00 and IGI. When thepotential difference across the line wires IE1! and IQI is at apredetermined value the winding I50 maintains the solenoid I59 and themovable contact I51 in the position shown in Figure 1. If the potentialdifierence across the line wires Iii!) and H11 should decrease to apredetermined low value, then the armature I59 and the contact I51 movedownwardly as shown in Figure 3 under the influence of springs, gravityor other means (not shown) to cause the movable contact I51 to engagethe stationary contact I55. An abutment surface I53 formed on the leverI65 prevents downward movement of the movable con.- tact I51 if thepotential difierence across the line wires I00 and IIII decreases afterthe overload cut-out mechanismhas been operated to separate the contacts85 and 85 as is clearly illustrated in Figure 2.

A bimetallc element I65 carried by the support I56 is adapted to engagea lug I51 carried by the lever I34, the bimetallic element I65 beingheated by a heater I66. The energization of the heater I66 is controlledby a relay I which may comprise an operating coil H! for moving switcharms I12 and I13 into engagement with contacts 114 and I15,respectively, when energized. When the operating coil I1I is deenergizedthe switch arms I12 and I13 are moved out of engagement with theirrespective contacts by means of springs, gravity or other means (notshown).

Assume now that the parts are in the position shown in Figure 1 and thatthe potential difference across the line wires I00 and Illl decreases toa predetermined value to cause the movable contact I01 to engage thestationary contact I55. If this decrease in potential differencepersists the current flow through the heater IZI will increase to causeoutward flexing of the bimetallic element I35 to separate the contacts85 and 86 and to close the contacts MI and I42, this movement beingpermitted by the pivotal connection I441 between the levers I34 and H16and the spring I118 as shown in Figure 3. Separating of the contacts 85and 86 stops operation of the compressor motor I8 and movement of thecontact I 31 into engagement with the contact M2 completes a circuitfrom the line wire I00, through wire I18, contacts I51 and I55, wiresI19 and I86, operating coil I11, wire IBI, contacts MI and M2, and wiresI82 and I25 back to the other line wire IIlI. Completion of this circuitcauses energization of the operating coil Hi to move the switch arms I12and 113 into engagement with their respective contacts.

Movement of the switch arm I12 into engagement with the contact I14completes a maintaining circuit for the operating coil I1I which may betraced. from the line wire I00 through wires I13 and I26, switch armI12, contact I1 1, wires I211 and 1311, operating coil I11, wire IBI,contacts MI and M2, and wires I82 and I25 back to the other line wireIEII. This maintaining circuit maintains the operating coil I'IIenergized until such time as the contacts MI and M2 are separated.Movement of the switch arm I13 into engagement with contact 115completes a circuit from the line wire 1% through wires H8, 119, andI83, switch arm I13, contact I15, wire I81, heater I65, and wire I backto the other line wire I131. Ccmpletion of this circuit energizes theheater element I66 which flexes the bimetallic element I65 upwardly tomove the lever I36 upwardly which in turn separates the contacts MI andM2 and recloses the contacts 55 and 86.

From the above it is seen that the overload cut-out mechanism SIoperates to separate the contacts 25 and 8% to stop operation of thecompressor when the current flow in the energizing circuit of thecompressor motor becomes excessive. If the excessive current flow in theenergizing circuit for the compressor motor is caused by a decrease inpotential difference across the power lines, the contacts and at will bereclosed automatically after they have once been opened, the length oftime required for automatically reclosing the contacts 35 and beingdetermined by the length of time required for the bimetallic element I65to move the lever I36 upwardly. If the excessive current flow in theenergizing circuit of the compressor motor should be caused by somethingother than a decrease in potential difierence,'the contacts 85 and 35are separated to stop operation of the compressor motor and they may bereclosed only by manual manipulation of the button I 5I. Automaticreclosing under these conditions is prevented by the abutment surfaceI63 on the lever I 15.

Since most of the overload conditions in a refrigerating apparatus arecaused by starting the compressor against relatively high head pressuresor by continuing the compressor in operation when the head pressurebecomes extremely high or the suction pressure becomes extremely low,the complete system outlined above obviates most of these conditions sothat the compressor motor I8 will seldom if ever become overloaded. Theother condition which causes excessive current flow through thecompressor motor is usually a decrease in potential difference acrossthe energizing circuit and since this is not a very serious condition itis desirable to automatically reclose the overload cut-out mechanismwhen the overload cut-out mechanism is opened by this condition. If anoverload condition other than those outlined above should occur thiswould be an indication that something was radically wrong with therefrigerating system and when the overload cut-out mechanism 6| stopsoperation of the compressor motor due to these other conditions,-manualresetting of the overload cut-out mechanism BI is required. This willindicate that the system should be checked for faulty operation.

From the above it is seen that this invention contemplates a completesystem for maintaining accurate temperature conditions in a plurality offixtures or zones, for defrosting the evaporators at each cycle ofoperation of the refrigerating apparatus, for insuring that theevaporators will defrost at least once during a predetermined timeinterval and for providing safe operation of the system. In this latterrespect the existence of extremely high pressures on the high pressureside of the refrigerating apparatus and extremely low pressures on thelow pressure side of the apparatus are prevented as well as overheatingof the compressor motor.

Although for purposes of illustration one form of this invention hasbeen disclosed, other forms thereof may become apparent to those skilledin the art upon reference to this disclosure and therefore thisinvention is to be limited only by the scope of the appended claims andprior art.

I claim as my invention:

1. In a control system for a refrigerating apparatus .having acompressor and evaporator means associated therewith for cooling a medium, the combination of, an electrically operated relay for operating thecompressor when energized and including a maintaining switch closed uponenergization of the relay, a first control device including a firstswitch and means responsive to pressure on the high pressure side of therefrigerating apparatus for closing and opening the first switch as thepressure respectively falls below or rises above a predetermined lowpressure value, a second control device including a second switch andmeans responsive to pressure on the high pressure side of therefrigerating apparatus for closing and opening the second switch as thepressure respectively falls below or rises above a predetermined highpressure value,

a third control device including a third switch and means responsive tothe pressure on the low pressure-side of the refrigerating apparatus forclosing and opening the third switch as the pressure respectively risesabove or falls below a predetermined high value, a fourth control deviceonly the maintaining switch and the second and fourth switches formaintaining the relay energized when the maintaining switch and thesecond and fourth switches are closed whereby the compressor ismaintained in operation until the pressure on the high pressure side ofthe refrigerating apparatus rises above the predetermined high value oruntil the pressure on the low pressure side of the refrigeratorapparatus falls below the predetermined low value.

2. In a control system for a refrigerating apparatus having acompressor. and evaporator means associated therewith for cooling amedi= um, the combination of, an electrically operated relay foroperating the compressor when energized and including a maintainingswitch closed upon energization of the relay, a first control deviceincluding a first switch and means responsive to pressure on the highpressure side of the refrigerating apparatus for closing and opening thefirst switch as the pressure respectively falls below or rises above apredetermined low pressure value, a second control device including asecond switch and means responsive to pressure on the high pressure sideof the refrigerating apparatus for closing and opening the second switchas the pressure respectively falls below or rises above a predetermined.high pressure value, a third control device including a third switch andmeans responsive to the pressure on the low pressure side of therefrigerating apparatus for closing and opening the third switch as thepressure respectively rises above or falls below a predetermined highvalue, a fourth control device including a fourth switch and meansresponsive to the pressure on the low pressure of the re including afourth switch and means responsive to the pressure on the low pressure.of the refrigerating apparatus for closing and opening the fourthswitch as the pressure respectively rises above or falls below apredetermined low value. a starting circuit for the electricallyoperated relay including only the first and third switches forenergizing the relay when both the first and third switches are closedwhereby the compressor is started when the pressure on the high pressureside of the refrigerating apparatus falls below the predetermined lowvalue and the pressure on the low pressure side rises above the pre- ,a

determined high value, and a maintaining circuit for the electricallyoperated relay including frigerating apparatus for closing and openingthe fourth switch as the pressure respectively rises above or fallsbelow a predetermined low value, a fifth control device including afifth .switch and means responsive to the temperature of the mediumbeing cooled for closing and open- I ing the fifth switch as thetemperature respectively rises above or falls below a predeterminedvalue, a starting circuit for the electrically operated relay includingonly the first, third and fifth switches for energizing/the relay onlywhen the first, third and fifth switches are closed, and a maintainingcircuit for the electrically operated relay including only themaintaining switch and the second, fourth and fifth switches formaintaining the relay energized until either the second, fourth or fifthswitches are opened.

3. In a control system for a refrigerating apparatus having a compressorand a plurality of evaporators for cooling medium in a plurality ofzones, the combination of, thermostatic control means for each zoneresponsive to the temperature of the medium being cooled of that zone,control means responsive to the pressure on the low pressure side of therefrigerating apparatus, means controlled by the control means and thethermostatic control means for starting operation of the compressor onlywhen any of the thermostatic control means calls for cooling and thepressureon the low pressure side of the refrigerating apparatus rises toa defrosting value and for continuing the compressor in operation untileither all of the thermostatic control means are satisfied or thepressure on the low pressure side of the refrigerating apparatusdecreases to low pressure side of the refrigerating apparatus will riseto a defrosting value at least at these predetermined times.

4. In a control system 'for a refrigerating apparatus having acompressor and a plurality of evaporators for cooling medium in aplurality of zones, the combination of, thermostatic control means foreach zone responsive to the temperature of the medium being cooled ofthat zone, control means responsive to the pressure on the low pressureside of the refrigerating apparatus, means associated with each zone andcontrolled by the thermostatic control means of that zone to admitrefrigerant to the evaporator of that zone upon a call for cooling bythe thermostatic control means of that zone, means controlled by thecontrol means and the thermostatic control means for starting operationof the compressor only when any of the thermostatic control means callsfor cooling and the pressure on the low pressure side of therefrigerating apparatus rises to a defrosting value and for continuingthe compressor in operation until either all of the thermostatic controlmeans are satisfied or the pressure on the low pressure side of therefrigerating apparatus decreases to a predetermined low value, andmeans operatively associated with said last mentioned means for stoppingoperation of the compressor at predetermined times whereby the pressureon the low pressure side of the refrigerating apparatus will rise to adefrosting value at least at these predetermined times.

5. In a control-system for a refrigerating apparatus having a compressorand a plurality of evaporators for coolng medium in a plurality ofzones, the combination of, thermostatic control means for each zoneresponsive to the temperature of the medium being cooled of that zone,control means responsive to the pressure on the low pressure side of therefrigerating apparatus, control means responsive to the pressure on thehigh pressure side of the refrigerating apparatus,

' means controlled by both of the control means and the thermostaticcontrol means for starting operation of the compressor only when any ofthe thermostatic control means call for cooling, the pressure on the lowpressure side of the refrigerating apparatus rises to a defrosting valueand the pressure on the high pressure side of the refrigeratingapparatus decreases to a predertermined low value and for continuing thecompressor in operation until either all of the thermostatic controlmeans are satisfied or the prespressure on the low pressure side of therefrigerating apparatus rises to a defrosting value and the pressure onthe high pressure side of the refrigerating apparatus decreases to apredetermined low value and for continuing the compressor in operationuntil either all of the thermostatic control means are satisfied or thepressure on the low pressure side of the refrigerating apparatusdecreases to a predetermined low value or the pressure on the highpressure side of the refrigerating apparatus increases to apredetermined high value, and means associated with said last mentionedmeans for stopping operation of the compressor at predetermined timeswhereby the pressure on the low pressure side of the refrigeratingapparatus will rise to a defrosting value at least at thesepredetermined times.

7. In a control system for a refrigerating apparatus having a compressorand a plurality'of evaporators for cooling medium in a plurality ofzones, the combination of, thermostatic control means for each zoneresponsive to the temperature of the medium being cooled of that zone,means associated with each zone and controlled by the thermostaticcontrol means of that zone to admit refrigerant to the evaporator ofthat zone upon a call for cooling by the thermostatic control means ofthat zone, control means responsive to the pressure on the low pressureside of the refrigerating apparatus, control means responsive to thepressure on the high pressure side of the refrigerating apparatus, meanscontrolled by both of the control means and the thermostatic controlmeans for starting operation of the compressor only when any of thethermostatic control means call for cooling, the pressure on the lowpressure side of the refrigerating apparatus rises to a defrosting valueand the pressure on the high pressure side of the refrigeratingapparatus decreases to a predetermined low value and for continuing thecompressor in operation until either all of the thermostatic controlmeans are satisfied or the pressure on the high pressure side of therefrigerating apparatus increases to a predetermined high value, andmeans associated with said last mentioned means for stopping operationof the compressor at predetermined times whereby the pressure on the lowpressure side of the refrigerating apparatus will rise to a defrostingvalue at least at these predetermined times.

8. In a control system for a refrigerating apparatus having a compressorand a plurality of sure on the high pressure side of the refrigeratingapparatus increases to a predetermined high value, and means associatedwith said last mentioned means for stopping operation of the compressorat predetermined times whereby the pressure on the low pressure side ofthe refrigerating apparatus will rise to a defrosting value at least atthese predetermined times.

6. In a control system for a refrigerating apparatus having a compressorand a plurality of evaporators for cooling medium in a plurality ofzones, the combination of, thermostatic control' means for each zoneresponsive to the temperature of the medium being cooled of that zone,

control means responsive to the pressure on the low pressure side of therefrigerating apparatus,

control means responsive to the pressure on the operation of thecompressor only when any of the thermostatic control means call forcooling, the

7 'high pressure side of the refrigerating apparatus, I means controlledby both of the control means and the thermostatic control'means forstarting evaporators for cooling medium in a plurality of zones, thecombination of, an electrically operated relay for operating thecompressor when en-. ergized and including a maintaining switch closedupon energization of the relay, thermostatically operated switch meansfor each zone responsive to the temperature of the medium being cooledof that zone and closed upon a call'for cooling, a first switch, meansresponsive to the pressure on the low pressure side of the refrigeratingapparatus for closing the first switch when the pres-' sure rises abovea defrosting value, a starting circuit for the electrically operatedrelay including the thermostatically operated switch means arranged inparallel with respect to each other and the first switch arranged inseries with the thermostatic'ally operated switch means for energizingthe relay only when any of the thermostatically operated switch meansare closed and the first switch is closed whereby the compressor isstarted only when at least one of the thermostatically operated switchmeans is calling for cooling and the pressure on the low pressure sideof the refrigerating apparatus has risen to a defrosting value, amaintaining circuit for the electrically operated relay including thethermostatically operated switch means arranged in parallel with respectto each other and the maintaining switch for maintaining the relayenergized and the compressor in operation until all of thethermostatically operated switch means are satisfied, a normally closedtime operated switch opened at predetermined times, said time operatedswitch being located in series with said thermostatically operatedswitch means for deenergizing the electrically operated relay andstopping operation of the compressor at predetermined times whereby thepressure on the low pressure side of the refrigerating apparatus willrise to the defrosting value at least at these predetermined tims.

9. In a control system for a refrigerating apparatus having a compressorand a plurality of evaporators for cooling medium in a plurality ofzones, the combination of, an electrically operated relay for operatingthe compressor when energized and including a maintaining switch closedupon energization of the relay, thermostatically operated switch meansfor each zone responsive to the temperature of the medium being cooledof that zone and closed upon a call for cooling, first and secondswitches, means responsive to pressure on the low pressure side of therefrigerating apparatus for closing the first switch when the pressurerises to a defrosting value and for opening the second switch when thepressure decreases to a predetermined low value, a starting circuit forthe electrically operated relay including the thermostatically operatedswitch means arranged in parallel with respect to each other and thefirst switch arranged in series with the thermostatically operatedswitch means for energizing the relay only when any of ththermostatically operated switch means are closed and the first switchis closed whereby the compressor is started only when at least one ofthe thermostatically operated switch means is calling for cooling andthe pressure on the low pressure side of the refrigerating apparatus hasrisen to a defrosting value, a maintaining circuit for the electricallyoperated relay including the maintaining switch, the thermostaticallyoperated switch means arranged in parallel with respect to each otherand the second switch for maintaining the relay energized and thecompressor in operation until either all of the thermostaticallyoperated switch means are satisfied or until the pressure on the lowpressure side of the refrigerating apparatus decreases to thepredetermined low value to open the second switch, a normally closedtime operated switch opened at predetermined times, said time operatedswitch being located in series with the thermostatically operated switchmeans for deenergizing the electrically operated relay and stoppingoperation of the compressor at predetermined times whereby the pressureon the low pressure side of the refrigerating apparatus will rise to thedefrosting value at least at these predetermined times.

10.In a control system for refrigerating apparatus having a compressorand a plurality of evaporators for cooling medium in a plurality ofzones, the combination of, an electrically operated relay for operatingthe compressor when energized and including a maintaining switch closedupon energization of the relay, thermostatically operated switch meansfor each zone responsive to the temperature of the medium being cooledof that zone and closed upon a call for cooling, first and secondswitches, means responsive to prescreases to a predetermined low valueand for opening the fourth switch when the pressure increases to apredetermined high value, a starting circuit for the electricallyoperated relay including the thermostatically operated switch meansarranged in parallel with respect to each other and the first and thirdswitches for energizing the relay only when any of the thermostaticallyoperated switch means are. closed and the first and third switches areclosed whereby the compressor is started only when at least one of thethermostatically operated switch means are calling for cooling, thepressure on the low pressure side of the refrigerating apparatus hasrisen to the defrosting value and the pressure on the high pressure sideof the refrigerating apparatus has decreased to the predetermined lowvalue, a maintaining circuit for the electrically operated relayincluding the thermostatically operated switch means arranged inparallel with respect to each other, the maintaining switch and thesecond and fourth switches for maintaining the relay energized and thecompressor in operation until either all of the thermostaticallyoperated switch means are satisfied or the pressure on the low pressureside of the refrigerating apparatus decreases to the predetermined lowvalue to open the second switch or the pressure on the high pressureside of the refrigerating apparatus increases to the predetermined highvalue to open the fourth switch, a normally closed time operated switchopened at predetermined times, said time operated switch being locatedin series with said thermostatically operated switch means fordeenergizing the electrically operated relay and stopping operation ofthe compressor at predetermined times whereby the pressure on the lowpressure side of the refrigerating apparatus will rise to the defrostingvalue at least at these predetermined times.

11. In a control system for a refrigerating apparatus having acompressor and a plurality of evaporators for cooling medium in aplurality of zones, the combination of, an electrically operated relayfor operating the compressor when energized and including a maintainingswitch closed upon energization of the relay, thermostatically operatedswitch means for each zone responsive to the temperature of the mediumbeing cooled of that zone and closed upon a call for cooling, meansassociated with each zone and controlled by the thermostaticallyoperated switch means of that zone to admit refrigerant to theevaporator of that zone upon a call for cooling by the thermostaticallyoperated switch means of that zone, a first switch, means responsive tothe pressure on the low pressure side of the refrigerating apparatus forclosing the first switch when the pressure rises above a defrostingvalue, a starting circuit for the electrically operated relay includingthe thermostatically operated switch means arranged in parallel withrespect to each other and the first switch arranged in series with thethermostatically operated switch means for energizing the relay onlywhen any of the thermostatically operated switch means are closed andthe first switch is closed whereby the compressor is started only whenat least one of the thermostatically operated switch means is callingfor opened at predetermined times, said time operated switch beinglocated in series with said thermostatically operated switch means fordeenergizing the electrically operated relay and stopping operation ofthe compressor at predetermined times whereby the pressure on the lowpressure side of the refrigerating apparatus will rise to the defrostingvalue at least at these predetermined times,

12. In a control system for a refrigerating apparatus having acompressor and a plurality of evaporators for cooling medium in aplurality of zones, the combination of, an electrically operated relayfor operating the compressor when energized and including a maintainingswitch closed upon energization of the relay, thermostatically operatedswitch means for each zone responsive to the temperature of the mediumbeing cooled of that zone and closed upon a call for cooling, meansassociated with each zone and controlled by the thermostaticallyoperated switch means of that zone to admit refrigerant to theevaporator of that zone upon a call for cooling by the thermostaticallyoperated switch means of that zone, first and second switches, meansresponsive to pressure on the low pressure side of the refrigeratingapparatus for closing the first switch when the pressure rises to adefrosting value and for opening the second switch when the pressuredecreases to a predetermined low value, a starting circuit for theelectrically operated relay including the thermostatically operatedswitch means arranged in parallel with respect to each other and thefirst switch arranged in series with the thermostatically operatedswitch means for energizing the relay only when any of thethermostatically operated switch means are closed and the first switchis closed whereby the compressor is started only when at least one ofthe thermostatically operated switch means is calling for cooling andthe pressure on the low pressure side of the refrigerating apparatus hasrisen to a defrosting value, a maintaining circuit for the electricallyoperated relay including the maintaining switch, the thermostaticallyoperated switch means arranged in parallel with respect to each otherand the second switch for maintaining the relay energized and thecompressor in operation until either all of the thermostaticallyoperated switch means are satisfied or until the pressure on the lowpressure side of the refrigerating apparatus decreases to thepredetermined low value to open the second switch, a normally closedtime operated switch opened at predetermined times, said time operatedswitch being located in series with the thermostatically operated switchmeans for deenergizing the electrically operatedrelay and stoppingoperation of the compressor at predetermined times whereby the pressureon the low pressure side of the refrigerating apparatus will rise to thedefrosting value at least at these predetermined times.

13. In a control system for a refrigerating apparatus having acompressor and a plurality of evaporators for cooling medium in aplurality of zones, the combination of, an electrically operated relayfor operating the compressor when energized and including a maintainingswitch closed upon energization of the relay, thermostatically operatedswitch means for each zone responsive to the temperature of the mediumbeing cooled of that zone and closed upon a call for cooling, meansassociated with each zone and controlled by the thermostatically,operated switch means of that zone to admit refrigerant to theevaporator of that zone upon a call for cooling by the thermostaticallyoperated switch means of that zone, first and second switches, meansresponsive to pressure on the low pressure side of the refrigeratingapparatus for closing the first switch when the pressure rises to adefrosting value and for opening the second switch when the pressuredecreases to a predetermined low value, third and fourth switches, meansresponsive to pressure on the high pressure side of the refrigeratingapparatus for closing the third switch when the pressure decreases to apredetermined low value and for opening the fourth switch when thepressure increases to a predetermined high value, a starting circuit forthe electrically operated relay including the thermostatically operatedswitch means arranged in parallel with respect to each other and thefirst and third switches for energizing the relay only when any of thethermostatically operated switch means are closed and the first andthird switches are closed whereby the compressor is started only when atleast one of the thermostatically operated switch means are calling forcooling, the pressure .on the low pressure side of the refrigeratingapparatus has risen to the defrosting value and the pressure on the highpressure side a of the refrigerating apparatus has decreased to thepredetermined low value, a maintaining circuit for the electricallyoperated relay including the thermostatically operated switch meansarranged in parallel with respect to each other, the maintaining switchand the second and fourth switches for maintaining the relay ener gizedand the compressor in operation until either all of the thermostaticallyoperated switch means are satisfied or the pressure on the low pressureside of the refrigerating apparatus decreases to the predetermined lowvalue to open the second switch or the pressure on the high pressureside of the refrigerating apparatus increases to the predetermined highvalue'to open the fourth switch, a normally closed time operated switchopened at predetermined times, said time operated switch being locatedin series with said thermostatically operated switch means fordeenergizing the electrically operated relay and stopping operation ofthe compressor at predetermined times whereby the pressure on the lowpressure side of the refrigerating apparatus will rise to the defrostingvalue at least at these predetermined times.

14. In a control system for a refrigerating apparatus having anelectrically operated compressor and a plurality of evaporator means forcooling medium in a plurality of zones, the combination of, anenergizing circuit for the electrically operated compressor,thermostatic control means for each zone responsive to the temperatureof the medium being cooled of that zone, controlv means responsive tothe pressure on the high pressure side of the refrigerating apparatus,control means responsive to thepressure on the low pressure side of therefrigerating apparatus, switch means controlled by the control meansand the thermostatic control means for controlling the energizingcircuit to start the compressor only when any of the thermostaticcontrol means calls for cooling, the pressure on the low pressure sideof the refrigerating apparatus rises to a defrosting value and thepressure on the high pressure side of the refrigerating apparatusdecreases to a predetermined low value and for continuing the compressorin operation until either all of the thermostatic control means aresatisfied or the pressure on the low pressure side of the refrigeratingapparatus decreases to a predetermined low value or the pressure on thehigh pressure side of the refrigerating apparatus increases to apredetermined high value, means associated with said switch means foropening the energizing circuit for stopping operation of the compressorat predetermined times whereby the pressure on the low pressure side ofthe refrigerating apparatus will rise to the defrosting value at leastat these predetermined times, overload means associated with said switchmeans and responsive to current flow in the energizing circuit foropening the energizing circuit upon the occurrence of excessive currentflow, means for manually operating the overload means for reclosing theenergizing circuit, and means responsive to the potential differenceacross the energizing circuit and operative upon opening of theenergizing circuit for automatically operating the overload means toreclose automatically the energizing circuit when the same has beenopened by an excessive current flow in theenergizing circuit caused by adecrease in potential diiference across the energizing circuit.

15. In a control system for a refrigeration apparatus having acompressor and a plurality of evaporators for cooling medium in aplurality of zones, the combination of, thermostatic control means foreach zone responsive to the temperature of the medium being cooled ofthat zone, control means responsive to the pressure on the low pressureside of the refrigerating apparatus, means controlled by the controlmeans and the thermostatic control means for starting operation of thecompressor only when any of the thermostatic control means calls forcooling and the pressure on the low pressure side of the refrigeratingapparatus rises to a defrosting value and for continuing the compressorin operation until all of the thermostatic control means are satisfied,and means operatively associated with said last mentioned means forstopping operation .of the compressor at predetermined times whereby thepressure on the low pressure side of the refrigerating apparatus willrise to a defrosting value at least at these predetermined times.

' GEORGE H. FISHER.

